The present invention is concerned with a skid-controlled brake system comprising a pedal-operated, preferably auxiliary force-supported, brake pressure generator. The brake pressure generator is connected to the wheel brakes via pressure fluid conduits. The brake system further comprises a hydraulic auxiliary pressure supply system including a hydraulic pump. a pressure accumulator, a pressure compensating and pressure fluid reservoir and an auxiliary pressure control valve. Also, the system includes wheel sensors and electronic circuits for detecting the wheel rotating pattern and for generating electric brake pressure control signals capable of controlling electromagnetically operable pressure fluid inlet and outlet valves provided in the pressure fluid conduits for skid control purposes.
A brake system of the afore-described type is disclosed, for example, in U.S. Pat. Nos. 4,415,210 and 4,416,491, wherein the brake pressure generator is a master cylinder including a hydraulic brake force booster coupled ahead thereof. The auxiliary pressure supply system contains a hydraulic pump and a hydraulic accumulator from which an auxiliary pressure proportional to the pedal force is admitted through a control valve upon applying the brake. Dynamic pressure is transmitted through the master cylinder to the static brake circuits connected to the master cylinder. The wheel brakes of one axle, preferably of the rear axle, are directly connected to the pressure chamber to which the pressure proportional to the pedal force is admitted through the control valve. For skid-control purposes, inlet valves are provided both in the static circuits and in the dynamic circuit, which inlet valves, normally, are switched to the passage position and through which, in the event of imminent locking of one wheel, the pressure fluid supply can be discontinued to the concerned wheel brake. Outlet valves are provided through which, if necessary, pressure fluid can be discharged from the wheel brake to the pressure compensating reservoir. Upon commencement of skid control, the booster chamber is in communication with the static brake circuits of the master cylinder through a so-called master valve in order to enable the pressure fluid discharged through the outlet valves to be re-fed to the static circuits. The structural details required for generating, storing and controlling the hydraulic auxiliary pressure, for the dynamic in-flow into the static circuits and for insuring the brake functions upon failure of individual circuits, are rather substantial.
The control signals for the inlet and outlet valves, in brake systems of the afore-described type are generated with the aid of electronic circuits the inlets of which are in communication with wheel sensors, for example, inductive transducers. The electronic circuits are capable of responding to a change in the wheel rotating pattern indicative of theh locking risk by keeping constant, reducing and reincreasing the pressure on the concerned wheel.